In communication systems, signaling transmission/reception is generally achieved between a fixed Base Station (BS) and a Mobile Station (MS) through a deep link (also referenced as a “hot link”), so a high-reliability radio communication link can be easily formed between the BS and the MS.
Presently, active research is being conducted to secure mobility of MSs and flexibility of wireless network configuration in the communication system and to provide more efficient services in the wireless environment where there is a significant change in the traffic distribution and the required amount of traffic. As one of the methods suggested by the research, a communication system can be considered, to which a data transfer scheme based on a multi-hop relay technology is applied using Relay Stations (RSs).
A communication system using the relay scheme (hereinafter referred to as a ‘relay communication system’) can reconfigure its network to rapidly cope with a change in the communication environment, and can efficiently operate the entire wireless network.
In addition, the relay communication system can expand its cell service coverage and increase the system capacity. For example, when a channel state between a BS and an MS is poor, an RS can be installed in a region where the channel state is poor, to form a relay path through the RS, thereby providing a wireless channel having a better channel state to the MS. Further, the relay scheme can be used in the cell boundary where the channel state to the BS is poor, to provide higher-rate data channels and expand the cell service coverage.
With reference to FIG. 1, a description will now be made of data transmission/reception periods in a relay communication system using a half-duplex scheme (hereinafter referred to as a ‘half-duplex relay communication system’).
FIG. 1 is a diagram illustrating data transmission/reception periods in a general half-duplex relay communication system.
As illustrated, FIG. 1 shows data transmission/reception periods for downlink data transmission/reception between a BS, an RS and an MS in a half-duplex relay communication system. In FIG. 1, solid lines represent transmission periods, while dotted lines represent reception periods.
The BS transmits first data S1 in a first time period t1, and transmits no data in a second time period t2.
The RS receives the first data transmitted by the BS in the first time period, and transmits second data S1′ generated using the first data to the MS in the second time period.
The MS can receive the first data transmitted by the BS in the first time period and can receive the second data transmitted by the RS in the second time period according to its location.
Resources of the half-duplex relay communication system can be defined as time. That is, in the first time period, the BS transmits the first data to the RS, and in the second time period, the RS transmits the second data generated using the first data to the MS.
In this case, the RS performs only one of data transmission and data reception in one time period, causing a reduction in resource-use efficiency for data transmission/reception. In order to address these problems, a relay communication system using a full-duplex scheme (hereinafter referred to as a ‘full-duplex relay communication system’) has been proposed to more efficiently use resources, and a frame structure in the full-duplex relay communication system is shown in FIG. 2.
FIG. 2 is a diagram illustrating data transmission/reception periods in a general full-duplex relay communication system.
As illustrated, FIG. 2 shows data transmission/reception periods for downlink data transmission/reception between a BS, an RS and an MS in a full-duplex relay communication system. In FIG. 2, solid lines represent transmission periods, while dotted lines represent reception periods.
The BS transmits first data S1 in a first time period t1, and transmits third data S2 in a second time period t2.
The RS receives the first data transmitted by the BS in the first time period, and transmits second data S1′ generated using the first data to the MS in the second time period. Further, the RS receives the third data transmitted by the BS in the second time period.
The MS, according to its location, can receive the first data transmitted by the BS in the first time period and receive the second data transmitted by the RS and the third data transmitted by the BS in the second time period. In other words, the full-duplex RS can simultaneously transmit and receive data.
With reference to FIG. 3, a description will now be made of a configuration of a general relay communication system.
FIG. 3 is a diagram illustrating a configuration of a general relay communication system.
Referring to FIG. 3, a relay communication system includes a BS 310, an RS 350, a first MS 351, and a second MS 353. Service coverage of the relay communication system can be indicated by coverage of a BS cell (BS's cell) 320 managed by the BS 310 and coverage of an RS cell (RS's cell) 360 managed by the RS 350. In addition, signals ‘a’, ‘b’ and ‘c’ transmitted by the BS 310 are shown. The signals ‘a’, ‘b’ and ‘c’ are transmitted simultaneously by the BS 310. The RS 350 receives the signal ‘b’ transmitted by the BS 310.
In addition, signals ‘x’ and ‘y’ transmitted by the RS 350 are shown in FIG. 3. The signals ‘x’ and ‘y’ are transmitted simultaneously by the RS 350. The RS 350 transmits the signal ‘x’ to the first MS 351 and the signal ‘y’ to the second MS 353.
Meanwhile, the first MS 351 is assumed to be included in the BS cell 320 or located in its adjacent region, and the second MS 353 is assumed to be located far enough from the BS cell 320 or located out of the service coverage 320 of the BS 310.
The second MS 353 receives the signal ‘c’ from the BS 310 while receiving the signal ‘y’ from the RS 350. In this case, the second MS 353 can receive the signal ‘y’ without interference caused by the signal ‘c’ transmitted by the BS 310, since the signal ‘c’ is lower in strength than the signal ‘y’.
In the general half-duplex relay communication system, the transmission time of the BS 310 is separated from the transmission time of the RS 350 as shown in FIG. 1, so the signals ‘a’ and ‘c’ do not interfere with each other. However, in the full-duplex relay communication system, since the first MS 351 receives the signal ‘a’ from the BS 310 while receiving the signal ‘x’ from the RS 350, the signal ‘a’ may act as interference to the signal ‘x’ in the first MS 351.
As described above, in the conventional full-duplex relay communication system, when an MS in communication with an RS is located in a place near the cell of a BS, the BS's signal may act as an interference signal for the MS.